#include <iostream>

bool &mark(void) {
    static bool m;
    return m;
}

void swap_by_reference(float &x, float &y) {
    float t = y;
    y = x;
    x = t;
}

void swap_by_pointer(float *x, float *y) {
    float t = *y;
    *y = *x;
    *x = t;
}